Tool



Sapt 29, v A. B. KHNZEL I 3 TOOL Filed March 26, 1931 1N VEN TOR.

ATTORNEYS.

Patented Sept. 29, 1936 UNITED STATES TOOL Augustus B. Kinzel,Beechhurst, N. Y., assignor, by,mesne assignments, to Union Carbide andCarbon Corporation, a. corporation of New York Application March 26,

3 Claims.

The invention relates to edged tools which are used for the cutting andscraping of metals and other materials, and especially to the productionof more durable cutting edges for such tools.

Steels having self-hardening properties imparted by the presence oftungsten or molybdenum in combination with manganese or chromium andcarbon,- generally known as high-speedsteels, .have been extensivelyused for cutting tools. When the steels are properlyheat treated byrapidly quenching from about 1900 F. to 2400" F. and reheating andholding them for a time at about 1050 F. to produce a martensiticstructure, they can be subjected to high temperatures such as red heatwithout marked transformation of the martensite or a marked loss inhardness. Vanadium is now generally used in these steels to improve thesoundness, hardness, and toughness.

It has been found that when vanadium is present in the high speed steelin amounts suflicient to constitute a nitride-promoting agent, and thetool is given a nitrided coating, the durability of the tool beco esremarkably improved. The exact reasons fo the improvement in the cuttingproperties of the tool are unknown to me, since it is commonly supposedthat nitriding decreases the toughness of the surface layers of a steel.It is my present belief that the nitriding increases so the red hardnessof the steel and that the increase of red hardness gives advantages inoutting tools which outweigh any disadvantages that may arise fromlosses of toughness resulting from the treatment. It is essential onlythat the working or' edged portion of the tool be given the hardstructure known as nitrided steel. This hard nitrogenous structure isproduced by introducing nitrogen at temperatures below 600 C. into thesurface layers of steels whichcontain nitride promoting agents.

The structure of the tools of my invention is to be more readilyunderstood by reference to the accompanying drawing, in which:

Figure 1 represents a typical metal-cutting tool,

Figure 2 represents a cross-section of the tool of Figure 1, taken alongthe plane 2-2,

Figure 3 represents another form of metalcuttlng tool, and 1 Figure 4represents an enlarged cross-section of the tool of Figure 3, takenalong the plane 4-4. 1

The cross-sectional diagram Figure 2 shows'a hard nitrided case 10, inexaggerated scale, formed of nitrided material of the same compo- 1931,Serial No. 525,623

sition as the metal of the core or body I l, the case I 0 covering onlya portion of the tool, as shown.

The cross-sectional diagram of Figure 4 shows a nitrided case I!completely encasing the body 5 metal l3.

The following description is illustrative of the invention. Lathe toolswere prepared from a bar of high-speed steel of the followingapproximate composition, tungsten 18.0%, chromium 4.0%, vanadium 1.0%,carbon 0.76%, and the remainder iron except small amounts of impurities.The tools were uniformly heat treated according to well known methods togive them hardness, and divided into two groups. The tools of the firstgroup were given a nitrided coating by heating them in ammonia to about.500 C. for 24 hours. The tools of the second group were not nitrided.The tools were tested by cutting semi-steel under like conditions. Itwas found 26 that the nitrided cutting edges gave about 45% more cuttingservice than the untreated tools.

A series of nitrided tools, known as threading chasers, of approximatelythe above composition was compared with a series of the same compositionwhich were not nitrided. It was found that the nitriding of the cuttingedges nearly doubled the life of the threading chasers.

'I'he term "high speed steel as used in the specification and claimsrefers to steels having the above described self-hardening properties.They contain about 0.25% to 1.2% carbon, generally not over 0.9% carbon;about 5% to 25% tungsten, generally between 7% and 21%; about 2% to 10%chromium, generally between 3% and 6%; and seldom over 0.4% manganese.Tungsten may be replaced by molybdenum but both tungsten and molybdenummay be present. Various other elements, such as cobalt and uranium aresometimes present. 40

According to the present invention the highspeed steel must containvanadium in solid solution in suflicient amount to constitute a nitridepromoting agent. As described in applicant's Patent No. 1,736,920, aminimum of approximately 0.3% to 0.5% of non-carbide vanadium isrequired in steel for this purpose. Large excesses of non-carbidevanadium may be present.

The total vanadium which is required in the steel to give this amount ofvanadium in solid solution cannot be stated exactly in terms of per-,centage. The vanadium content depends on the carbon content of thesteel and the presence of other carbide forming elements, such astungsten, molybdenum, and chromium which combine with some of thecarbon. Higher carbon contents require more vanadium to give non-carbidevanadium It may be stated that the high speed steel which constitutesthe base metal or core of the tool should contain more than about 0.4%vanadium to give good nitriding but a large excess of hon-carbidevanadium is not detrimental. Amounts of non-carbide vanadium which areproduced by the presence of about 1.0% of vanadium with the lower carbonselfhardening steels and about 1.5% of vanadium with the higher carbonsteels give excellent results.

It is evident that the invention may be embodied in various kinds ofedged tools and it is to be understood that the invention is not limitedto the embodiments of the invention which have been specificallydescribed or shown in the accompanying drawing.

I claim:-

1. An edged cutting tool suitable for cutting metal and comprising abody portion of high speed steel containing about 0.25% to 1.2% carbon,about 7% to 21% metal of the group consisting of tungsten andmolybdenum, about 2% to 10% chromium, and vanadium in amount sufficientto give at least about 0.3% non-carbide vanadium; and a. working edge,the outer layers of said working edge being composed of nitrided bodymetal.

2. An edged lathe tool comprising a body portion of high speed steelcontaining about 0.25% to 0.9% carbon, about 7% to 21% metal of thegroup consisting of tungsten and molybdenum, about 3% to 6% chromium,vanadium in amount sufiicient to give about 0.4% to 1.5% non-carbidevanadium, the remainder principally iron; and a working edge, the outerlayers of said working edge being composed of nitrided body metal.

3. An article of manufacture embodying an alloy consisting of iron withabout 0.70% carbon, about 18.00% tungsten, about 4.00% chromium. about1.00% vanadium and having a surface nitrided.

AUGUSTUS B. KlNZEL.

